Robert Love posted in his blog some interesting screenshots: Thanks to beaglefs, a FUSE-based filesystem written by him that creates a real filesystem subtree from the results obtained from a beagle query) he was able to get a "people" subdirectory, with subdirectories named as your contacts, icons, and inside every directory links to all the documents related with that contact.

Well, you _can_ save searches in Gnome since Nautilus got some search integration. On my FC5 it works with the Beagle backend by default, but in theory the backend is pluggable, and I think a working alternative is the "tracker" project search.

It's not right there in your face, though, so in the eventuality that it just slipped under your radar:
1) Open any folder, so that you have a Nautilus menu
2) Places > Search (or CTRL+F)
3) Build your query adding the criteria you're interested in
4) File > Save Search
There, you've got your "virtual folder".

There's been some discussion on the mailing list about the best way to make this process easier and much more visible to end users.
Of course this is an abstraction at Filemanager level, much different from a FUSE virtual directory, but having a swappable backend has some convenience. We'll see how it all comes together.
/K